I am looking to build a dirt jump track and after realizing how much dirt is really required for a proper jump I am exploring using a wood frame to pile dirt on top of to reduce the need for dirt. I live in San Diego with little rain, so it seems this is as good a climate as there is to use wood without being overly concerned about the wood going bad or rotting or decomposing. My plan was to build a bridge more or less with about 18-24 inch "hand rail/walls." I would then fill the dirt in over the bridge up to the top of the wall (so the dirt would be about 18-24 inches thick) so there is a table top with a take off and landing I can sculpt. I was going to use pressure treated lumber when possible for structural integrity/longevity, set the posts of the bridge in concrete, and use sealed plywood where necessary. It seems this would be very solid.
If it lasts 3 years, I would be happy. I suspect it will last longer than that in San Diego. Questions:
Has anyone seen this/have any feedback?
Is 18-24 inches enough dirt to properly compact and hold? I would think so as I have seen small 24 inch tall jumps and they don't fall apart.
Any thoughts on pressure treated lumber lasting a long time in contact with dirt that will need to be lightly watered somewhat frequently? I've seen posts saying pressure treated wood should last decades in contact with the ground.